Vehicle fuel use and emissions (FU&E) have substantial national energy and environmental implications, but are confounded by sources of intra/inter-vehicle variability and, therefore, require scientific inquiry in order to develop an improved basis for their characterization and management. The main objectives of this research are to: (1) quantify intra-vehicle variability in FU&E due to inter-driver variability, cold start, ambient conditions, and road grades; (2) develop FU&E models based on multiple levels of vehicle aggregation and multiple temporal scales; and (3) evaluate the interface of these models with transportation models and for use with real-time vehicle detection.